Contact adhesives differ from other adhesives, such as pressure sensitive adhesives, in that the adhesives are applied to both substrates to be joined and then dried. These adhesives are characterized by a bonding range or "open time", i.e., the period after the adhesive is dry during which adhesive coated substrates can be successfully joined and bonded. Contact adhesives are used to manufacture decorative laminates.
Environmental regulations require a reduction in solvent emissions in the decorative laminate industry. Solvent based neoprene contact adhesives, the industry standard, are a primary source of these emissions. Attempts have been made to reduce solvent volatiles through the use of aqueous contact adhesives. Such aqueous adhesives have been only marginally successful. Also, most of the aqueous adhesives do not provide the same bond strength as solvent-based systems.
U.S. Pat. No. 3,565,247 discloses a pressure sensitive adhesive tape, the adhesive layer of which is a foam.
U.S. Pat. No. 4,415,615 discloses a cellular pressure sensitive adhesive membrane comprising 15-85% voids that does not collapse after being briefly compressed. The adhesive product is preferably made by the steps of
(1) frothing a composition which is polymerizable to a pressure sensitive adhesive state,
(2) coating the froth onto a backing, and
(3) polymerizing the coated froth in-situ to a pressure sensitive adhesive state.
GB No. 2,135,903 discloses a foamed pressure sensitive adhesive layer having a stable foam structure prepared by mixing a gas comprising oxygen with an aqueous dispersion comprising an unsaturated polyester, a pressure sensitive adhesive component and an accelerator comprising an organic compound effective for oxidative curing of the polyester. The formulations are preferably frothed with air.
U.S. Pat. No. 4,561,918 discloses foaming a vinyl acetate-ethylene copolymer based adhesive to extend the adhesive and thereafter applying it to the tips of the medium flutes subsequent to the corrugation of the medium. A liner is then applied to the glued medium to produce a single faced corrugated product.
U.S. Pat. No. 4,713,263 discloses a foamable, storage-stable flocking adhesive prepared from an aqueous emulsion of a vinyl acetate/ethylene/N-methylol comonomer copolymer.